WO2013037671A2

WO2013037671A2 - Charging circuit for a capacitance and method for charging a capacitance

Info

Publication number: WO2013037671A2
Application number: PCT/EP2012/067205
Authority: WO
Inventors: Mario Teufel
Original assignee: Ams Ag
Priority date: 2011-09-16
Filing date: 2012-09-04
Publication date: 2013-03-21
Also published as: EP2795760B1; WO2013037671A3; EP2795760A2; DE102011113641A1

Abstract

In one embodiment, a charging circuit for a capacitance has a first connection (8) for supplying a supply voltage (Vbat), a second connection (9) for connection to the capacitance (SC), a charging switch (S) which is coupled to the first and second connections (8, 9), and a temperature unit (TMU) with an output (13) which is coupled to a control input of the charging switch (S). The temperature unit (TMU) is set up to control the charging switch (S) on the basis of a difference between an instantaneous temperature (Tist) of the charging circuit and an adjustable upper limit value temperature (Tlimit) of the charging circuit. A method for charging the capacitance is also stated.

Description

description

Charging circuit for a capacity and method for charging a capacity

The invention relates to a charging circuit for a capacity and a method for charging the capacity.

In many applications, capacities are used as charge storage. An example of this is the operation of a flash ^¬ light. The charge cached in the capacitance is provided at the moment the flash is fired, for example, to a flash light emitting diode. To make this possible, he ^¬, the charge storage must be charged to the required voltage first. For charging such a capacity, different methods are known. A possible ^¬ ness is the capacitance by means of a connected thereto in series resistance, which has a limited capacity of the supplied charging current to charge. Another option is to charge the capacitance directly from a power source with a defined current. Both options, taking into account thermal conditions, result in a relatively long charging time. One known way of a charging circuit for a Kapa ^¬ capacity is shown in FIG. 1 Here, the charging takes place with the aid of a current source Iq, which is supplied by a voltage source and the capacity C provides a charging current in a certain amount. In an example in which the current source Iq supplies a current of 1 A, in which the value of the capacitance is 512 mF and a voltage of 4.4 V is provided by the voltage source, the relationship arises

where I is the value of the charging current, C is the value of the capacitance and U is the value of the voltage, the charging time t is a value of

2.25 s. Thus, it takes 2.25 seconds to charge the capacitance C from 0V to the value of the battery voltage Vbat, namely 4.4V. FIG. 2 shows the associated time profile of the power loss P. The generated power loss is initially 4.4 W and s has the value 0 W ^¬ it is sufficient to 2.25. FIG. 3 shows the associated profile of the temperature T of the circuit used for charging in ° C. in relation to time t. From Figure 3 it can be seen that the temperature reaches a maximum value of 230 ° C, which is well above the thermal limit of silicon chips. Experi ^¬ has shown silicon chip have a thermal limit, which is about 180 ° C. The option set to load the La ^¬ dung storage would therefore destroy the chip thermally.

An object is thus to provide a circuit and a method to cross with the or with the La ^¬ is accelerated capacity without thermal Gren ^¬ zen.

The object is solved with the subjects of the independent claims. Further developments and refinements are each objects of the dependent claims. In one embodiment, a charging circuit for a capacitor comprises a first terminal for supplying a supply voltage, a second terminal for connecting to a capacitor, a charging switch connected to the first and to the second terminal is coupled to a Temperaturein ^¬ unit. The temperature unit includes an output coupled to a control input of the charging switch. The temperature unit is configured to control the charging switch as a function of a difference between a current temperature of the charging circuit and an adjustable upper limit temperature of the charging circuit.

At the beginning of the charging process, the charging switch is closed so that the supply voltage is supplied to the capacity via the charging switch. The supplied power, which results from the supply voltage and a charging current that arises across an internal resistance of the charging switch or a series resistance of the charging switch, leads to an increase in the instantaneous temperature of the charging circuit. The temperature unit controls the charging switch so that the adjustable upper limit temperature is not exceeded during the charging process. As soon as the difference between the current temperature and the upper limit temperature has reached zero, the charging switch is opened. Then be ^¬ starts to fall again, the current temperature and the charging switch is closed again. This is repeated until the capacity is charged to a setpoint at the end of a charge cycle.

The fact that the charging switch is controlled as a function of the difference between the current temperature and the upper limit temperature, the connectable capacity is charged as quickly as possible and without exceeding the thermal limits.

The charging switch has an internal resistance. The upper limit temperature is dependent on the adjustable technology and materials used. When implemented using silicon, 144 ° C is an example of the upper limit temperature. In a further development, the temperature unit has a comparator with hysteresis. The comparator comprises a first switching threshold as a function of the upper limit temperature and a second switching threshold as a function of a lower limit temperature.

The hysteresis of the comparator results in a delaying of the reconnection of the charging switch after the upper one

Limit temperature has been reached. The charging switch is thus closed again only when the current temperature has fallen to the value of the lower limit temperature.

With the help of the hysteresis function of the comparator charging can be set with advantage so that the Aufla ^¬ the capacity always follows the thermal limit of the charging circuit and always with the maximum possible temperature ^stroke he ^¬ . This leads to an acceleration of the charging process.

Due to the reuse of existing components such as the comparator, the charging switch and the generation of hysteresis no additional chip area is needed.

In a further embodiment, the comparator has a first input, a further input and an output. The first input is supplied with an actual value signal as a function of the instantaneous temperature. The further input is supplied in dependence of the temperature upper limit ^¬ an upper limit signal. At the output is a control signal as Function of the difference between the actual value signal and the upper limit signal provided.

The feedback signal representing the instantaneous temperature, while the upper limit value signal represents the upper limit temperature ^¬ structure. The control signal, which is generated as a function of the difference between the actual value and the upper limit signal from the comparator, controls the charging switch. On the one hand, the present charging circuit takes into account the thermal resistance of the charging circuit and, on the other hand, its thermal dew. The specified in the unit Kelvin per watt ^¬ ne thermal resistance indicates which temperature deviation generates the supply of power loss in a certain amount. Thus, the thermal resistance provides information about ^¬ represents that power loss cope with a circuit. The final temperature of a circuit which is reached due to the supply of a power loss of a certain amount, thus results as the sum of the current temperature of the circuit and the product of the value of the power loss and the thermal resistance.

The time behavior is determined by the thermal dew. The thermal tau, which is expressed in seconds, is a measure of how long the circuit takes to reach a final temperature due to the power supplied and the thermal resistance. After three thermal dew 95% of the final temperature is reached, while after five thermal dew 99% of the final temperature are reached. In a development, the charging circuit has a temperature sensor, which is connected to the first input of the comparator and thermally coupled to the charging circuit, on. The temperature sensor provides the feedback signal.

In a further embodiment, the temperature sensor has a diode with a defined temperature coefficient.

One way of implementing the temperature sensor is thus the use of a diode with a known temperature behavior. The voltage drop across the diode changes depending on the temperature.

In a further development, the limit ^{signal is} supplied as an adjustable reference voltage.

The reference voltage is set to represent the upper limit temperature.

In one embodiment, the temperature unit for Steue ^¬ tion of the charging switch is arranged such that is charging ^¬ switch closed when the feedback signal is smaller than the upper limit value signal that the charging switch is opened when the actual value is greater than the upper limit value ^¬ signal and that the charge switch remains open until the instantaneous temperature represented by the feedback signal is again lower than the lower limit temperature.

In a further embodiment, the charging switch comprises a transistor. The transistor has a defined internal resistance, which limits the charging current supplied to the charging current during the charging process. In an alternative embodiment, the charging switch comprises an ideal switch without internal resistance and a current source coupled to this switch.

In one embodiment, a circuit arrangement has a charging circuit described above and the capacity. The

Capacitance is connected to the second terminal of the charging circuit and to a reference potential terminal.

The capacitance is realized, for example, as a supercapacitance, which realizes a high capacitance value over a small area and has a low internal resistance. This is particularly advantageous in the application as Zwischenspei ^¬ cher of charge for a flash light emitting diode. In one embodiment, a method for charging a capacitor comprises the following steps:

- supplying a charging current in response to a versor ^¬ supply voltage via a charging switch a charging circuit to the capacitance,

Determining a current temperature of the charging circuit,

Comparing the current temperature with an upper limit temperature, and

- controlling the charging switch as a function of a difference between the instantaneous temperature and the upper limit value temperature, until the capacity is charged at the end of a Ladezyk ^¬ lus to a desired value.

The fact that the upper limit temperature of the charging circuit is taken into account when charging, the capacity is always charged at the thermal limit of the charging circuit. This advantageously allows a very fast charging in the context of the thermal conditions of the charging circuit. The method additionally adapts to variable variables such as, for example, the level of the supply voltage, the level of the instantaneous temperature of the charging circuit, the thermal situation in the vicinity of the charging circuit and the like. The process ensures that charging is always carried out at the highest possible speed.

The method can be implemented particularly cost-effective and space-saving without digital control.

In a further development of the driving of the Ladeschal- carried ters such that the charging switch is closed if the current temperature is less than the upper limit temperature ^¬ structure that the charge switch is opened when the current temperature reaches the value of the upper limit temperature, and that the charging switch is closed again when the current temperature is less than the lower limit temperature.

These steps reflect the above already beschrie ^¬ bene hysteresis of the comparator used again.

In a further embodiment the driving of the load switch is such that the charging switch is opened at the end of La ^¬ dezyklus or remains closed. At the end of a charging cycle, which is determined by the fact that the capacity is charged to the desired value, which is adapted to the level of the supply voltage, for example, the charging switch is opened or remains closed.

The invention will be explained in more detail with several Ausführungsbei ^¬ games with reference to FIGS. Functional rela ^¬ hung as effectively identical components and circuit parts bear like reference numerals. Insofar as circuit parts correspond in function, their description is not repeated in each of the figures. Show it:

1 shows an example of a charging circuit of the prior art,

FIG. 2 shows an exemplary course of the power loss from the prior art, FIG. 3 shows an exemplary temperature profile from the prior art,

FIG. 4 shows a first exemplary embodiment of a charging circuit according to the proposed principle,

5 shows another exemplary embodiment of a charging circuit according to the proposed principle,

FIG. 6 shows an exemplary diagram for explaining the hysteresis of the comparator,

FIG. 7 shows exemplary diagrams for explaining the thermal dew, 8 shows explanatory diagrams for explaining the charging ^¬ circuit according to the proposed principle, Figure 9 is exemplary diagrams for charging by means of current ^¬ source according to the prior art, and

FIG. 10 shows exemplary diagrams when charging via a ^resistor according to the prior art.

FIG. 4 shows a first exemplary embodiment of a charging circuit according to the proposed principle. The charging circuit comprises a first terminal 8, to which a supply voltage Vbat is supplied, a second terminal 9 for connection to a capacitor SC, a charging switch S and a temperature unit TMU. The charging switch S is coupled to the first and second terminals 8, 9 and has an internal resistance Ri. The temperature unit TMU has an output 13, to which a control signal En is provided, which is supplied to a control input of the charging switch S. The temperature unit TMU comprises a comparator Cmp. The comparator Cmp is supplied via its first input 11, a current temperature Tact the charging circuit. Via its further input 12, the comparator Cmp is supplied with an adjustable upper limit temperature Tlimit. The connectable capacitance SC is connected to its other An ^¬ circuit with a reference potential terminal 10. At the capacitance SC is applied to a voltage V_scap. By way of example, the capacitance SC has a supercapacitance with a capacitance value which is very high in relation to the area, for example in the mF range, and has a low internal resistance. At the start of a charge cycle, the charge switch S CLOSED ^¬ sen is. The capacitance SC is supplied to a charging current Ic as a function of the supply voltage Vbat versor ^¬ via the further terminal 9 of the charging circuit. The capacity SC charges up. The current temperature T ist of the charging circuit starts to increase. As soon as the instantaneous temperature Tact reaches the value of the upper limit temperature Tlimit, the value of the control signal En changes at the output 13 of the temperature unit TMU, whereby the charge switch S is opened. The current temperature Tist drops. If the instantaneous temperature Tact has reached the value of an adjustable lower limit temperature, the charging switch S is closed again and the capacitance SC is charged further with the aid of the charging current Ic. This process is repeated until the voltage V_scap at the capacitor SC is charged to a desired value. This target value is adjusted, for example, at the height of the versor ^¬ supply voltage Vbat. Upon reaching the set point, at the end of a charge cycle, the charging switch S remains closed ge ^¬.

The control of the charging switch S and thus the entire load cycle ^¬ place as a function of the difference between the current temperature Tact and the upper limit temperature Tlimit the charging circuit. Due to this temperature-dependent control is achieved with the greatest possible advantage of the speed of charging the capacitance SC, wherein thermal boundary ^¬ values such as the upper limit temperature Tlimit are not exceeded. Figure 5 shows another exemplary embodiment ei ^¬ ner charging circuit according to the proposed principle. In addition to the embodiment of Figure 4 here is the temperature unit TMU and the external wiring of the charging circuit shown in more detail. The temperature unit TMU comprises, in addition to FIG. 4, a temperature sensor TS and a voltage source for providing an adjustable reference voltage Vdc. The temperature sensor TS is connected on the one hand to the first terminal 8 of the charging circuit and on the other hand to the reference potential terminal 10. The tempera ^¬ tursensor TS includes a current source for providing a current Idc and a diode D. The diode D is coupled to the power source.

At constant current, the diode D has a constant over a wide temperature range temperature coefficient of, for example, -2 mV / K. Accordingly, a voltage Vd dropped across the diode D decreases by 2mV as the temperature increases by 1K according to the following equation:

Vd _{^ 2} mV

dT ~ K

Here, Vd represent the voltage Vd at the diode D, -2 mV / K the temperature coefficient of the diode D and dT the change of the instantaneous temperature Tact of the charging circuit.

The voltage Vd dropping at the connection point between the current source and the diode D of the temperature sensor TS is supplied as an actual value signal Vtemp_actual to the first input 11 of the comparator Cmp. The comparison voltage Vdc is the comparator Cmp at its second input 12 as the upper limit signal

Supplied to Vtemp_cmp. The comparator Cmp is as shown a comparator with

Hysteresis, which has a first switching threshold and a second switching threshold. The first switching threshold is represented sent from the upper limit signal Vtemp_cmp, which is a measure of the upper limit temperature Tlimit. The second switching threshold of the comparator CMP is set in Depending ^¬ ness of a lower limit temperature. The

Hysteresis of comparator Cmp is detailed in Figure 6 be attributed ^¬.

The external circuitry of the charging circuit comprises a power source Bat, which provides the supply voltage Vbat and the capacitance SC.

The charging circuit forms together with the capacitance SC a circuit arrangement according to the proposed principle. 6 shows an exemplary diagram for explaining hysteresis of the comparator of Figure 4 and 5. On the X axis is the instantaneous temperature Tist is shown, while the Y-axis of the control signal En repre sented ^¬ at the output of the comparator. The control signal En assumes values between zero and one. On the X-axis are the two switching thresholds of the

Comparator located, namely, the upper limit temperature Tlimit Tempe ^¬ and the lower limit temperature Tu. Des Wei ^¬ direct an ambient temperature Tamb is located, which represents the temperature of the environment of the charging circuit.

As described earlier, at the beginning of a charge cycle, the charge switch S is controlled by the control signal En is stale ^¬ tet, as can be seen from the ascending branch of the switching function shown. As a result, the supply voltage Vbat is switched to the second terminal 9 of the charging circuit and the capacitance SC begins to charge. The instantaneous temperature Tact increases, as can be seen from the rightward branch of the illustrated switching function. As soon as the instantaneous temperature Tis the value of the upper limit temperature Tlimit Tempe ^¬ reached, the charging switch S is opened by the control signal En or off according to the falling branch of the switching function. Consequently, the temperature Tist falls according to the left-hand branch of the switching function. As soon as the instantaneous temperature Tact reaches the value of the lower limit temperature Tu, the control signal En at the output of the comparator Cmp switches from zero to one, whereby the charging switch S is closed and the illustrated switching function is run through again. Has reached its desired value of the capacitance the voltage on Schaltfunkti ^¬ is exited at any point.

The value of the upper limit temperature Tlimit is determined as a function of the semiconductor material used in the circuit. The value of the lower limit temperature Tu is freely definable in an interval between the ambient temperature Tamb and the upper limit temperature Tlimit. By choosing a value of the lower limit temperature Tu, which is above the ambient temperature Tamb, it is ensured that the capacitance SC is fully charged.

FIG. 7 shows exemplary diagrams for explaining the thermal dew. The upper diagram shows the curve of the power P supplied to a circuit in units of watts. The lower diagram shows two different profiles of the mo ^¬ mentanen temperature Tist in degrees Celsius. The example shown is based on a charging circuit with a thermal resistance of 40 K / W, which is supplied with a power of 1 W for 2 s. The initial temperature is 85 ° C. For the curve marked 1, the value is the thermal Toff 100 ms, whereas in the marked with 2 ^¬ plotted curve reflects the value of the thermal Toff be 200 ms ^¬. It can be clearly seen that in curve are reached after 300 ms 1 95% of the end ^¬ value of 125 °, ie 123 ° C, while supplying the same power this value is reached in curve 2 until 600 ms. The charging circuit according to the proposed principle limits the power supplied to the capacity to be charged, both in terms of their height and in terms of their duration, taking into account the thermal characteristics of the charging circuit and thus advantageously achieves the highest possible charging speed.

Figure 8 shows exemplary diagrams for explaining the La ^¬ circuit according to the proposed principle. The individual diagrams are shown in the course of time t in seconds. The first line shows the course of the control signal En. The second line shows the course of the current temperature Tact in degrees Celsius. The third line shows the course of Ver ^¬ supply voltage Vbat and the voltage V_scap on the capacitance in volts. The fourth line shows the course of the charging current Ic in amperes. The fifth line shows the course of the supplied power P in watts.

The switching on and off of the supplied power P or the charging current Ic and the resulting fluctuation of the temperature Tist between a lower limit temperature of 140 ° C and an upper limit temperature of 144 ° C can be clearly seen. This corresponds to a hysteresis of 4 ° C. The voltage V_scap at the capacity meanwhile rises steadily. Charging is completed after 4.2 s when the capacity is charged to an exemplary 4V setpoint. FIG. 9 shows exemplary diagrams when charging by means of a current source according to the prior art. In the respective lines of the diagrams, with the exception of the first line, the same sizes are shown as in FIG. 8, so that a comparison is possible. The first line shows the activation of the charging process by means of a signal On. When ^¬ conven tional loading by means of a power source, such ^¬ example, with the circuit of Figure 1, the charging current Ic is supplied continuously. In order not to destroy the circuit thermally, however, only a charging current Ic of about 350 mA can be supplied. Thus, the voltage V_scap on the capacitor is charged to the same value as in FIG. 8 only after the much longer time of 5.8 s.

FIG. 10 shows exemplary diagrams when charging via a resistor according to the prior art. Again, the same sizes are shown as in Figure 9. Here, a resistor limits the maximum supplied charging current Ic. The value of the resistor is for example 12 Ω. The capaci ^¬ ty is here only after 15 s some charged to the desired value to. A reduction of the resistance value is not mög ^¬ Lich, otherwise the larger charging current Ic would result in a thermal cerium ^¬ interference of the charging circuit according to it.

The diagrams make it clear once again that the proposed charging circuit and the proposed method allow a much faster charging of the capacitor without causing thermal damage to the circuit. Reference sign list

1, 2 curve

8 - 11 connection

Cmp comparator

D diode

S charging switch

Ri internal resistance

Tist, Tlimit temperature

Tu, T temperature

V_scap, Vbat voltage

Vd, Vcmp voltage

Vdc, V9 voltage

En control signal

TS temperature sensor

TMU temperature unit

Ic charging current

C, SC capacity

Vtemp cmp; Vtemp_actual signal

Bat energy source

Idc electricity

Iq power source

On signal

Claims

Charging circuit for a capacity comprising

a first terminal (8) for supplying a supply voltage (Vbat),

a second connection (9) for connection to the capacitance (SC),

a charging switch (S) coupled to the first and second terminals (8, 9), and

- a temperature unit (TMU) having an output (13) which is connected to a control input of the charging switch (S) gekop ^¬ pelt,

wherein the temperature unit (TMU) is arranged to control the La ^¬ deschalters (S) in response to a difference between a current temperature (TIST) of the charging circuit and an adjustable upper limit temperature (Tlimit) of the charging circuit.

Charging circuit according to claim 1,

wherein the temperature unit (TMU) comprises a comparator (Cmp) with hysteresis and wherein the comparator (Cmp) ei ^¬ ne first switching threshold depending on the upper

Limit temperature (Tlimit) and a second switching ^¬ threshold in response to an adjustable lower limit temperature (Tu).

Charging circuit according to claim 2,

the comparator (Cmp)

a first input (11), which is an actual value signal

(Vtemp_actual) is supplied as a function of the instantaneous temperature (Tist), - a further input (12) to which a threshold signal (Vtemp_cmp) depending on the upper limit value tempera ture ^¬ (Tlimit) is supplied, and

- An output (13) to which a control signal (En) as a function of the difference between the actual value signal

(Vtemp_actual) and limit signal (Vtemp_cmp) is bereitge ^¬ provides,

having .

Charging circuit according to claim 3,

further comprising a temperature sensor (TS) connected to the first input (11) of the comparator (Cmp) and thermally coupled to the charging circuit.

Charging circuit according to claim 4,

wherein the temperature sensor (TS) comprises a diode (D) having a predetermined temperature coefficient.

Charging circuit according to one of claims 3 to 5,

where the limit signal (Vtemp_cmp) as adjustable

Comparison voltage (Vdc) is supplied.

Charging circuit according to one of claims 2 to 6,

wherein the temperature unit (TMU) for controlling the La ^¬ deschalters (S) is arranged such that the charge ^¬ switch (S) is closed when the actual value signal (Vtemp_actual) is smaller than the upper limit signal (Vtemp_cmp), and that the charging switch (S) is opened when the actual value signal (Vtemp_actual) is greater than the upper limit signal (Vtemp_cmp), and that the charging switch (S) remains open until the instantaneous temperature represented by the actual value ^¬ signal (Vtemp_actual). tur (Tist) is again smaller than the lower limit value Tempe ^¬ temperature (Tu).

Charging circuit according to one of claims 1 to 7,

wherein the charging switch (S) comprises a transistor.

Circuit arrangement with a charging circuit according to one of claims 1 to 8,

further comprising the capacitance (SC) which is connected to the two ^¬ th connection (9) of the charging circuit and a Bezugspo- tentialanschluss (10).

Method for charging a capacitor, comprising the following steps:

Supplying a charging current (Ic) as a function of a supply voltage (Vbat) via a charging switch (S) of a charging circuit to the capacitor (SC),

Determining a current temperature (Tist) of the charging circuit,

- Compare the current temperature (Tist) with an upper limit temperature (Tlimit), and

- Controlling the charging switch (S) in response to a difference between the current temperature (TIST) and the upper limit temperature (Tlimit), until the capacity (SC) is charged at the end of a charging cycle to a nominal ^¬ value.

Method according to claim 10,

wherein the driving of the charging switch (S) takes place such that the charging switch (S)

- is closed when the current temperature (Tact) is less than the upper limit temperature (Tlimit), - is opened when the current temperature (Tist) reaches the value of the upper limit temperature (Tlimit), and

- is closed again when the current temperature (Tist) is less than a lower limit temperature (Tu).

Method according to claim 11,

wherein the driving of the charging switch (S) is such that the charging switch (S) ge ^¬ opens at the end of a charge cycle or remains closed.